1103 


SEP    261922 


1103 


SERVICE  HANDBOOK 


OF  THE 


ETER,  MODEL  OF  1916 


PREPARED  IN  THE  OFFICE  OF 
THE    CHIEF    OF    ORDNANCE 


April,  1922 


WASHINGTON 
GOVERNMENT  PRINTING  OFFICE 

1922 


CEBTIFICATE:  By  direction  of  the  Secretary  of  War,  the  matter  contained 
herein  is  published  as  administrative  information  and  is  required  for  the  proper 
transaction  of  the  public  business. 


WAR  DEPARTMENT 

Document  No.  1103 

Office  of  The  Adjutant  G.eneral 


WAK  DEPARTMENT, 

WASHINGTON,  April  13, 

The  following  publication,  entitled  "  Service  Handbook  of  the 
Altimeter,  Model  of  1916,"  is  published  for  the  information  and 
guidance  of  all  concerned. 
[A.  G.  062.1  (3-28^-22).] 

BY  ORDER  OF  THE  SECRETARY  OF  WAR  I 

JOHN  J.  PERSHING, 

General  of  the  Armies, 

Chief  of  Staff. 
OFFICIAL  : 

ROBERT  C.  DAVIS, 

Acting  The  Adjutant  General. 
•  (m) 


491575 


CONTENTS. 


Page. 
General   description 1 

Instructions  for  mounting. 
Function  and  operation. 
Detailed  description 5 

Battery  commander's  station  instrument. 

Distant  station  instrument. 

Adjustments ' 6 

Nomenclature-1-  7 


ILLUSTRATIONS. 


PLATE    I.  Battery  commander's  station  instrument-- 2 

II.  Distant  station  instrument 4 

(iv) 


/ 


GENERAL  DESCRIPTION  OF  THE  ALTIMETER, 
MODEL  OF  1916. 


The  altimeters,  model  of  1916,  are  instruments  employed  in  anti- 
aircraft gunnery  to  measure  the  height  of  the  target  above  the  fire- 
control  station  by  projecting  its  altitude  into  the  vertical  plane  con- 
taining the  base  line  of  the  bilateral  stations.  Two  instruments  known 
respectively  as  the  battery  commander's  and  distant  station  instru- 
ments are  required  and  are  placed  one  at  each  end  of  a  base  line  of 
known  length.  This  model  of  altimeter  has  been  superseded  by  alti- 
meters, models  of  1917  and  1920  (War  Dept.  Doc.  No.  1105). 

INSTRUCTIONS  FOR  MOUNTING. 

The  procedure  in  establishing  both  instruments  for  operation  is 
similar.  Each  has  its  individual  packing  chest  and  canvas  hood, 
while  the  tripods  are  carried  separately.  The  tripod  legs  are  spread 
and  set  firmly  into  the  ground,  after  which  the  staff  bushing  support 
is  inserted  into  the  head  and  clamped.  The  instrument  is  then  re- 
moved from  its  chest,  placed  in  the  support  and  the  three  leveling 
screws  manipulated  until  the  bubbles  of  the  spirit  levels  are  in  the 
center  of  their  run.  The  instruments  are  oriented  either  by  use  of  the 
magnetic  compass  or  upon  some  point  common  to  both  stations.  On 
the  battery  commander's  station  instrument,  the  necessary  corrections 
are  made  for  length  of  base  line  and  difference  in  elevation  of  base 
end  stations,  after  which  the  instruments  are  ready  for  operation. 

FUNCTION  AND  OPERATION. 

The  principle  upon  which  this  type  of  altimeter  is  operated  is 
termed  direct  altimetry  (as  distinguished  from  indirect  altimetry) 
and  employs  what  is  commonly  known  as  the  "  roof  principle  "  where 
the  height  of  the  target  is  obtained  by  projecting  its  position  into  the 
vertical  plane  passing  through  the  base  line. 

In  setting  up  the  instruments,  the  orientation  error  should  not 
exceed  5  mils.  If  there  is  a  difference  in  elevation  between  base  end 
stations,  P  and  O,  Figure  1,  a  correction  is  made  hv  setting  the  full 

99225—22 2  m 


PLATE  I 


ALTIMETER,  MODEL  OF  1916. 

Battery  Commander's  Station  Instrument. 


correction  on  the  battery  commander's  station  instrument.  Thus,  if 
the  distant  station  is  found  to  be  500  yards  higher  than  the  battery 
commander's  station  instrument,  the  elevation  slide  is  clamped  within 
the  guides  of  the  base  length  slider  to  the  graduation  —5  on  the 
vertical  scale.  This  correction  reproduces  the  altimeter  triangle  in 
smaller  scale  on  the  instrument. 

A  represents  the  target  position  and  B  its  horizontal  projection 
into  the  vertical  plane  passing  through  the  base  line  PO.  The 
altitude  of  A,  therefore,  will  be  the  same  as  that  of  B.  By  means 
of  the  telescopes,  two  planes  of  sight  are  directed  on  the  airplane  A 

A 


Fig- I- 

and  the  angles  $1  and  ^  which  they  make  with  the  horizontal,  are 
measured  simultaneously.  The  angle  read  at  0,  180° — $2,  is  trans- 
mitted to  the  battery  commander  station  instrument.  The  operator 
there  swings  the  protractor  alidade  about  its  axis  until  this  angle 
registers  with  the  index  line  on  the  alidade  support.  The  protractor 
alidade  is  previously  set  in  a  direction  opposite  to  the  distant  station 
and  at  a  distance  from  the  center  of  the  horizontal  axis  of  the  pri- 
mary alidade  equivalent  to  the  length  of  the  base  line.  The  scale 
bears  a  proportion  to  the  base  line  of  1  to  40,000. 

When  the  angle  $2  from  the  distant  station  has  been  set  on  the 
instrument  and  the  telescope  of  the  battery  commander's  station 
trained  on  the  target,  the  altitude  of  the  target  is  read  from  the 
altitude  plate  at  the  intersection  of  the  two  alidades. 


PLATE  II 


ALTIMETER,  MODEL  OF  1916. 

Distant  Station  Instrument. 


DETAILED  DESCRIPTION  OF  THE  BATTERY  COM- 
MANDER'S STATION  INSTRUMENT. 

The  staff  (18)  which  is  the  main  support  of  the  instrument,  seats 
and  rotates  in  the  staff  bushing  (4).  The  bushing  in  turn  seats  in 
the  staff  bushing  support  (21)  in  the  manner  of  a  ball  and  socket, 
allowing  it  motion  in  all  directions  by  manipulation  of  the  three 
leveling  screws  (15).  The  lower  end  is  so  shaped  that  when  the 
leveling  screws  are  adjusted,  the  bushing  is  held  in  its  seat  as  well 
as  leveled.  An  arm  attached  by  screws  to  the  upper  surface  of  the 
bushing,  bears  an  engraved  index  line  for  reading  azimuth  gradua- 
tions and  accommodates  the  locking  stud  holding  the  index  clamp 
and  thumb  nut  (10).  The  staff  bushing  support  is  inserted  in  the 
head  of  the  tripod  (24)"  furnished  with  the  instrument,  which  is 
of  French  design  and  manufacture.  » 

A  flange  on  the  staff  supports  the  azimuth  dial  (7),  the  latter 
bearing  graduations  in  mils  around  its  circumference.  It  also  has 
engraved  on  its  top  surface  a  scale  of  amplitude  ±16°,  over  which 
the  pointer  on  the  compass  box  (6)  passes.  A  slotted  hole  provides 
means  for  quickly  attaching  or  detaching  the  compass.  The  dial  is 
secured  to  the  under  surface  of  the  flange  while  on  it's  upper  surface 
is  mounted  two  spirit  levels  (9)  set  at  right  angles  to  each  other. 

The  upper  portion  of  the  staff  has  a  bracket  extension  mounting 
the  altitude  plate  support  (19)  to  which  the  altitude  plate  (12)  is 
attached.  The  latter,  a  rectangular  brass  plate,  has  engraved  upon 
its  face  parallel  lines  numbered  from  10  to  50  and  corresponding 
to  altitudes  ranging  from  1,000  to  5,000  yards.  Above  the  plate 
and  on  the  center  line  of  the  staff  is  finished  a  horizontal  bearing 
in  which  the  telescope  axis  (3)  turns.  A  support  (22)  mounting 
an  observation  or  elbow  telescope  (23)  is  attached  to  one  end  of 
the  axis. 

A  vertical  axis  through  the  support  terminating  at  its  lower  end 
in  a  handle  (8)  provides  for  movement  of  the  telescope  in  elevation 
and  twisting  of  it  in  the  plane  of  site.  A  collimator  (5)  is  supported 
by  a  bracket  clamped  to  the  telescope  tube  to  aid  in  quickly  bring- 
ing the  line  of  sight  on  the  target. 

Affixed  to  the  opposite  end  of  the  telescope  axis  in  a  direction  at 
right  angles  to  the  line  of  sight,  is  the  primary  alidade  (1)  which 
moves  over  the  altitude  plate  upon  rotation  of  the  telescope  about 
the  horizontal.  A  spring  clutch  is  interposed  between  the  telescope 
and  alidade  in  order  that  the  alidade  might  be  shifted  so  that  it  will 
always  register  against  the  plate  whether  the  airplane  is  "  coming " 
or  "  going." 


The  bracket  at  the  upper  end  of  the  staff  is  also  provided  with  a 
slot  in  which  the  base  length  slider  (16)  can  be  moved  a  distance 
proportional  to  the  length  of  the  base  line  between  stations.  A  scale 
engraved  from  15  to  50,  corresponding  to  1,500  to  5,000  yards,  ap- 
pears above  the  slot,  against  the  graduations  on  which  the  slider  is 
set  and  clamped  by  a  wing  nut.  This  slider  has  a  vertical  slot 
graduated  ±  5,  representing  hundreds  of  yards  in  difference  of  sta- 
tion level.  In  this  slot  an  elevation  slider  (17)  is  guided  and  when 
conditions  require,  is  clamped  by  wing  nut  (11)  against  the  gradua- 
tion corresponding  to  the  difference  in  height  between  stations.  The 
elevation  slide  has  pivoted  to  it  the  protractor  alidade  support  (20) 
to  which  is  secured  the  protractor  alidade  (2).  The  support  projects 
beyond  the  right  side  of  the  protractor,  forming  an  index  against 
which  the  mil  scale  on  the  protractor  is  read.  The  protractor  bears 
an  arm  or  alidade  which  in  conjunction  with  the  primary  alidade 
forms  an  intersection  at  which  the  altitude  is  read  from  the  altitude 
plate. 

DISTANT  STATION  INSTRUMENT. 

The  lower  half  of  the  distant  station  instrument  is  identical  with 
the  battery  commander's  station  instrument.  The  staff,  however,  is 
shorter  and  terminates  at  its  upper  end  in  a  horizontal  bearing  fin- 
ished to  receive  the  telescope  axis  (3).  One  end  of  the  axis  mounts  a 
semicircular  protractor  (14)  graduated  in  mils  to  correspond  with 
the  protractor  alidade  on  the  battery  commander's  station  instru- 
ment, while  the  opposite  end  has  attached  to  it  a  support  to  which  is 
clamped  an  observation  telescope.  Like  the  battery  commander's 
station  instrument  the  telescope  may  be  moved  in  angle  of  sight  as 
well  as  twisted  in  the  plane  of  sight.  A  collimator  secured  to  a 
bracket  clamped  to  the  telescope  aids  in  directing  the  telescope  on  the 
target.  For  reading  angles  of  sight  from  the  protractor,  an  index 
plate  (13)  is  attached  by  screws  to  the  staff. 

ADJUSTMENTS. 

Both  the  battery  commander's  and  distant  station  instruments  are 
so  machined  and  assembled  in  the  shop  that  no  field  adjustments  are 
required.  However,  care  must  be  exercised  in  handling  the  alidades 
as  they  are  not  of  such  rugged  construction  that  they  will  with- 
stand bending  forces. 

A  set  screw  passing  through  the  support  and  bearing  against  the 
tube  of  the  telescope  permits  adjustment  of  the  horizontality  and 
verticality  of  the  reticule. 


NOMENCLATURE. 


To  assist  in  identifying  parts  of  the  instruments  the  following  list 
is  provided  and  numbers  corresponding  to  parts  enumerated  therein 
are  marked  on  Plates  I  and  II : 


1.  Alidade,  primary. 

2.  Alidade,  protractor. 

3.  Axis,  telescope. 

4.  Bushing,  staff. 

5.  Collimator. 

6.  Compass,  magnetic. 

7.  Dial,  azimuth. 

8.  Handle. 

9.  Levels. 

10.  Nut,  thumb. 

11.  Nut,  wing. 

12.  Plate,  altitude. 


13.  Plate,  index. 

14.  Protractor. 

15.  Screws,  leveling. 

16.  Slider,  base  length. 

17.  Slider,  elevation. 

18.  Staff. 

19.  Support,  altitude  plate. 

20.  Support,  protractor  alidade. 

21.  Support,  staff  bushing. 

22.  Support,  telescope. 

23.  Telescope. 

24.  Tripod. 


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PAT.  JAH  21,  1908 


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